Automatic voltage control system for alternators



June 13,1944!- F. F. HUTCHINSON 2,351,340

AUTOMATIC VOLTAGE CONTROL SYSTEM FOR ALTERNATORS Filed Dec. 10, 1941 v 22 INVENTOR. Fzwrou z? f/UTCH/NSON aroma);

Patented June 13, 1944 AUTOMATIC VOLTAGE CONTROL SYSTEM FOR. ALTERNATORS Fenton F. Hutchinson, San Francisco, Calif., as-

signor to Kohlcr & Chase, San Francisco, Calif., a corporation of California Application December 10, 1941, Serial No. 422,346

4 Claims.

The. invention, in general, relates to means for compensating for the voltage drop in a transmission or distribution line supplied by an alter-. nator; More particularly, the invention relates to a. combination of electrical units for main taining a substantially constant voltage at. the alternator, or at the terminals of the work cir-. cuit supplied thereby, regardless of load variations.

. Considerable effort has been devoted in recent years by those skilled in the art toward the pro vision of means and methods for increasing the efiiciency of alternators and towards the elimination or reduction of excessive wear upon the various, electrical units and parts of an alternate ing current generating system. One of the more difficult problems encountered in practically all of such systems is that of compensating for the drop in voltage in the work circuit under varying. resistance-reactance loads. While some measure of success has been attained in the solution of this problem where only resistance loads are connected into the work circuit, or under load conditions wherein the power factor is substantially unity or does not vary appreciably, there has been but indifferent success in maintaining. a substantially constant voltage at the terminals of the work circuit. where wide variations in power factor occur and where varying inductive loads are connected therein. In nearly all of the recently developed systems that have performed their intended functions with any deree of success, a constantrsupervision of the system and the presence of attendants is required for adjusting commutator brushes or the commutating plane, adjusting tap points on transformers, or the substitution of transformer coils to meet the varying load conditions, and this is especially truein such systems wherein the power factor variation extends .beyond predetermined limits for which the system has been constructed. The. present invention is directed to obviating the foregoing and other difiiculties encountered in alternating current generating systems under all conditions of load, and particularly where the load consists of variable inductances.

-A primary object of my invention is to provide an alteranting current generating system affording automatic regulating means for compensatfor the voltage drop in an alternating current work circuit due to the connection thereinto of variable resistance-reactance loads, and regardless of the power factor value of the work circuit.

Another object of the present invention is to provide a system of the aforementioned character which does not require the shifting of the commutator plane of any unit, and which does not require supervision or the presence of an attendant.

A still, further object of the invention is to provide an improved system of the indicated nature which is additionally characterized by a minimum of electrical units.

Another object of my invention is to provide an improved alternating current generating system. in which no arcing at commutator brushes occurs, and undue wear upon brushes and commutator segments is avoided.

The foregoing and other objects are attained in a preferred embodiment of my invention which is diagrammatically illustrated in the accompanying drawing. It is to be understood that while the accompanying drawing depicts a pre ferred embodiment for single phase operations, the invention is suitable for adaptation in embodiments operating in poly-phase as well, and it also is to be understood that I am not to be limited to the precise embodiment shown, nor to the precise arrangements of the several units thereof, as my invention, as defined in the appended claims, can be, embodied in a plurality and variety of forms.

Referring to. the drawing:

The single view is a schematic showing of the various electrical units and circuits of a preferred embodiment of my invention, as exemplified in a system operating in single phase.

In its preferred form, the automatic voltage control system for alternators of my invention preferably comprises, in combination with an alternator, an exciter for supplying the field of the alternator with direct current of varying magnitude; said exciter including an auxiliary field, together with means for deriving a variable potential from the work circuit supplied by the alternator, and means for rectifying the derived, variable potential and applying the rectified, derived potential to the auxiliary field of said exciter whereby the exciter variably excites the field of the alternator.

As illustrated in the accompanying drawing, my improved automatic voltage control system for alternators consists of but four electrical units, with their attendant leads and parts, inclusive of the alternator, which is designated in the drawing generally by the reference numeral I I. In addition to the alternator, the system includes a specially wound exciter l2 for supplying a direct current of varying magnitude to the field of the alternator 'll a specially wound currentv transformer l3 for deriving a variable potential from the circuit supplied by the alternator II; and a specially constructed direct current generator or converter M for rectifying the variable potential derived from the alternator work circuit and for applying the rectified, derived potential to the auxiliary field of the exciter I2, so that the exciter in turn will furnish adirect current of variable magnitude to the field of the alternator I I. This system, as hereinabove generally described, has been successfully employed in automatically maintaining a substan tially constant voltage at an alternator, or at drawing an alternator ll of a;type having four field poles l6, l1, l8 and I9 arranged in "opposed pairs, each pole carrying a single winding or main field coil 2|, 22, 23 and 24, respectively. It

is of course to be understood that the present invention canbe embodied in alternators havin any desired number of pairs of field poles, and that the armature of the'alternatorcan be wound for either single phase or polyphase operations. Moreover, it is clear-that it is optional whether the alternator armature be mountedfor rotation about fixed poles, or whether the field poles be arrangedfor rotation about a fixed armature. In the embodiment of the invention illustrated, the alternator comprises fixed field poles with its armature mounted'for rotation about the poles upon a driven shaft 25. As is customary, the current produced-by the alternator may be collected by suitable brushes 26 and 21'bearing upon collector rings 28 and 29, respectively, to which the terminals of the alternator armature winding are fastened; the collector rings being connected to but insulated from the armature shaft 25. The work or load circuit supplied by the alternator under single phase operation, in-

cludes two trunks or mains 3| and 32 leading from the brushes 26 and 21, respectively.

The fields of the alternator H are supplied with direct current from the speciallywound exciter |2 which may be of a type which includes four field poles 36, 31, 38 and 39 each of which carries a main field coil 4|, 42, 43 and 44, respectively, together with shunt windings 46, 41, 48 and 49, respectively. A suitable resistance, not shown, may be connected into the exciter shunt circuit for regulating the exciter. to the indicated shunt and series or main field windings, each of the field poles 36 to 39, inclusive, is provided with an auxiliary field coil 5|, 52, 53 and 54, respectively and such' coils are wound in directions opposite to the series and shunt windings and, hence, are of opposite polarity thereto. While the armature of the exciter I2, may,'if desired, be mounted on shaft upon which the alternator armature is mounted, the exciter armature nevertheless can be secured to a separate driven shaft 55 with'equivalent re sults. In view of the connections, as shown, direct current flows from the exciter commutator brush 56 through a; lead 51 connected to alter- In addition nator field coil 2|, thence through the several alternator fields; thencethrough a lead 56 connecting alternator field coil 24 to the series wind-'- ings of the exciter; thence backto exciter commutator brush 59 through a lead 60' from main exciter field'coil to complete the circuit. Since tween the auxiliary field coils of the exciter, on the one hand, and the shunt andseries windings thereof, on the other hand, issuch that variations from the predetermined value of current flowing in the auxiliary field coils of the exciter, as a result of load variations in the work circuit supplied by the alternator and of the combination of electrical units of my present improved system,

.are balanced b corresponding or proportional variations in the current flowing in the shunt and series windings of the exciter; and this balance is always maintained regardless of the type of load connected into the work circuit and regardless of the power factor characteristics of such work circuit; 'As a result of the maintenance of this balance in the exciter l2, voltage variations in the alternatorwork circuit are airtomatically compensated for, and the voltage on the alternator or at the terminals of its work circuit, is maintained substantially constant at the predetermined no load value. As is well 1111-? derstood, the foregoing applies both to flat-compounding and over-compounding, the only'difference between the latter and the former being that once a definite value of over-compounding has been decided upon it is only necessary to wind the exciter coils as well as the coils of trans-- former l3 initially to effect such value of over compounding. Once such coils are wound for either flat or over-compounding, there need not be any alternation thereof whatsoever for a' given capacity of alternator.

As illustrated in the accompanying drawing, my improved system includes a specially wound current transformer I3 comprising a saturated leg with an iron shunt including an airgap between an input or primary coil 6| and an output or secondary coil 62. As shown, the input 6| of transformer I3 is connected across the work circuit supplied by the alternator H by means of a pair of leads 63 and 64, while the terminals of the output 62 of transformer l3 are connected to leads 66 and 61 which are connecteditothe fields of regulator M as hereinafter described. It is clear that since the input or primary 6| .of transformer I3 is always across the load circuit, the currentflowing in transformer |3v under no load conditions is entirely magnetizing current which produces an E. M. F. in the output or sec ondary 62 that is always in direct proportion to the voltage of input 6|. It also is clear that this construction of transformer l3, as thus far described, imposes a definite limit to the current which may be withdrawn from the secondary 62 so that any attempt to withdraw current in 'ex-j cess of such limit merely results in the terminal voltage dropping to such an extent that only limited current flows therefrom. Hence, since the output of transformer |3 supplieslthe fields of regulator l4 and thelatter, in turn, feeds the auxiliary fields of exciter l2, the current flowing in said auxiliary fields of thei'exciter under no load conditions will have a predetermined value and is just suificient, with respect to the current flowing in the shunt and series windings of the exciter, with its armature movin'g' at a constant R. P. M., to maintain the "directcui- I3 is provided with an additional or tertiary coil 68 which is disposed on the saturated legof the transformer between its input 6| and its-output 62. Moreover, the tertiary coil- 68 is connected in series with the load and: with the alternator I I by means of the leads 69- and 10, as shown. As a result of the disposition of tertiary coil 68 on the saturatedleg oftransformer l3, as: shown,

and of the foregoing connections thereof into the load and alternator circuit, the amount of current flowing in-the tertiaryilwill have adirect influence upon the magnitude and phase of the current, appearing at: the terminals of'the output 62 of the transformer.

As indicated above, my improved system includes means for'utilizing: the variablepOten tial derived from the work circuit by transformer I3 for variably exciting the auxiliary fields of the exciter l2,'whereby'the fields of the alternator H are supplied with direct; current of variable magnitude in direct response to load variations. These means preferably include a specially constructeddirect current generator or regulator I4, the fields of which are supplied with alternating current ofvariable potential from the output. (i2 of: current transformer l3 through the leads 66 and 61; together with means for rectifying.- the derived" potential and applying the-same as a.- rectified, pulsating direct current to the auxiliary coils 5'! to 54 inclusive of the exciterv l2, As schematically shown at the left. center" of the drawing, the

regulator I4 includesxacorresponding number of pairs of field polesasthe alternator II, which in the present embodiment is two pairs or four poles; such field poles of the-regulatorl4 being designated generally by thereference numerals l6, l1, l8 and 19. Each-of: these field. poles is each of the. four' defined air gapsebetweenthe faces are. approximatelytwo-thirds the length of a fieldpole face. and these-dimensions, as well asthelengths of thezfield pole. faces, are critical;

The generator 14, moreover, is preferably provided with an armaturevwindingwhichis divided generally, into-four distinct and separate coils, designated by the numerals 86, 81, 88 and 89,

and each of these armature coils-is. preferably equal to the. dimensions of'a field pole face; such dimensions alsobeing critical. The armature of regulator I 4 is preferably: mounted. upon shaft upon which the alternator armature is mounted although, if: desired, such regulator armature maybe mounted: on a separate shaft 99so long as such shaftv is driven synchronously with shaft 25. tion, the output voltage of'the regulator l4, as conditioned by transformer I3; is rectified and applied to vary the'excitation of the, auxiliary field coils of .theexciter: 12'. To this, end; the terminals of the armature coils 86- to 99 inclusive of the regulator areconnected preferably to eight segments of a; rectifying commutator 9!, the commutator segments beingelectrically connected together in alternate. pairssoasto make practically atwo-part commutator. The, rectifying commutator 91:15 mountedion shaft 90'and the: voltage. as. thus modified; is taken off the Inaccordance with my inven-- commutator 9| by brushes 92 and 93, bearings thereon, to appear rectifiedas a pulsating direct current voltage applied to the leads 94 and 95 connected to thebrushes 92- and 93, respectively; such direct current voltage being of variable magnitude and phase depending upon the magnitude and phase of the load. As shown, the rectified current of variable potential produced by the regulator or converter I4 is supplied directly to the auxiliary field coils 51 to 54 inclusive, and to this end the several auxiliary coils areconnected together by means of the leads 96; 91- and' 98; and the lead 94 is connected to auxiliary field coil 54 while the auxiliary field coil 5| is connected to lead 95 connecting to brush 93 of the regulator-commutator, to complete the circuit;

The effect upon the fields of the regulator l4 of the disposition of tertiary-coil 68 between the input and output'of transformer I3, and of connecting such tertiary-coil inseries with the load and with the alternator depends-of course, upon thepresence or non-presence of a load in the work circuit of the alternator. Moreover, the effect of th specially =constructed regulator upon the auxiliary field's of theexciter depends upon the presence or non-presence of a load in the alternator work circuit, Under no load conditions, the E. M. F. produced at the terminals of the output 62 ofthe transformer I3 is in direct proportion to the voltage of the transformer input 6!, since the latter-is always across the work circuit. Moreover, thevoltage at rectifying commutator 9| of the regulator l4, under no-load conditions, is such that-the produced current of the regulator, which is fed tothe auxiliary field coils of the exciter, is always sufficient to maintain the correct or predetermined voltage on the exciter. It may be observed here that when maximum voltage appears at the commutator of the exciter I2, minimum current flows in the exciter series and shuntawindings and maximum current flows in the auxiliary field coils 5| and 54 inclusive so that thecorrectvoltage isproduced and this voltage balance .is maintained so long as there isno changeof potential in. the work circuit supplied bythealternaton However, when the voltage applied tolthe'fieldsjl to.84 inclusive of the regulator drops, as a:.result of a load being connected into; the alternator" work circuit,

the bucking potential at rectifying commutator 9i also drops, and the current flowing to and in the auxiliary field coils.5| toi5.4 inclusive of the.

exciter is reduced, thereby-permittingan increased current to flow. in the series and shunt windings of the exciter. Consequently, .theexciter will produce promptly the needed current to. feed the alternator fields andbringthevoltage of the alternator to its-no. load value, Clearly,,when the load is removed fromthe-alternator work circuit, the reverse of the above occurs, in that the terminal voltage of the. transformer output rises which, in turn, increases .the field strength of the regulator so that. the produced current of the regulator is increased and an increased current flows in the auxiliary field coils of the exciter, with a corresponding decreased, current flow in the series and shuntiwindings thereof, thus maintaining the balance or relationship therebetween.

It will be understood. from the-drawing that the automatic variable excitation-of the auxiliary field coils of the exciter l2 by, the-produced direct current of variable potentialsupplied. from regulator Missimilar whether the: load connected into thealternator work-1 circuit 'is-a pure resistance', a pure inductance, or a combination. of

these types ofloads. Dueto the special construc tion'of the regulator M with its armature winding concentrated asshownand eachof the four divisions of such armature winding equal indimension to a field pole face aswell as the dispositionof the tertiarytdotthe transformer 13 betweenits input and its output,- the regulator J4 so functions that as thepower factor characteristics, of the work. circuit approaches unitythe current produced by the regulator jl4 increases, and asv the power factor of the load circuit decreases, -the produced current of the regulator decreases. v 1.

. As indicated. above, the present improvement is entirelysuitable for poly-phase operations with but slight changes in connections; Ina threephase system, for example,,the transformer [3 would be duplicated and connections made for the alternator circuit thereto corresponding to the. connections for single phase in that the inputs of the two transformers would be connected across the three-legs ofthe alternator work circuit, and the tertiary coils of the .two transformers would be connectedin series with the load as well as the armature by suitable leads to two brushes on the alternator collectorrings. Of course, the alternator armature wouldbe wound in threephase rather than single phase but it would not be necessary to wind the' regulator armature for three-phase and the armature winding of regulator l4 could be used without change. The two transformeroutputs would be coupled together and connected incircuit with the regulator field or, if desired, two fields of two poles of the regulator 14 could be connected to on transformer output and the other two fields connected to the other transformer outputa Animportant advantage of my present improved system over standard or conventional alternating current generator circuits is that the commutatinghplane of, the converter M is perfeet when the converter. is producing its maximum current in its armature circuit. Consequently, any'lowering of the current in the armature circuit due to a weakening of the converter field strengthghas no appreciable efiect uponthe commutator planeand no arcing at the commutator brushes 92 and 93, or wearing of the segments of the commutator occurs. Moreover, the .Lcommuta'torbrushes are not required to be adjusted and no supervision of any kind is required.- Another'important'fature of this improved system is that no re-winding or rematching of transformercoils is required nor any transformer tap adjustments, for the system operates automatically to compensate for variations of potential in the work circuit supplied by the alternator regardless of the type of load that maybe connected therein up to the "maximumcapacity of the alternator.

It'is to be'understood'that the appended claims are to be accorded a' range of equivalents commensurate in scope with the advance made over the prior art.

I claim:

I 1 An automatic voltage control system for alternators comprising, in combination with an alternator, an exciter for supplying the field of the alternator with direct current of variable magnitude; said exciter including shunt and series -field windings as well as an auxiliary field coil of opposite polarity to the polarity of said shunt and series windingsysaid series field winding of said exciterbeing connected in seriescircuit relation with thefield of; the alternator and with the exciterarmature winding, means,

forderiving a variable;potential from the work. circuit supplied .bythe alternator, a regulator the field of which iszelectrically connected to said means, and 1a rectifying commutator on th shaft of said regulator for rectifying the de-,

rived, variable potential obtained from the alternator work circuit by said means and for reduc-,

field windings as well as; an auxiliary field of opposite polarity to. the polarity ,of said shunt. and series windings; said; series field, winding of said exciter being connected in series-circuit:

relation with the field of the alternator and with the exciter armature winding, :3. current trans.- former including an input, coil' connected across the work circuit supplied ,by the/alternator, an.

output coil, and a tertiary coil between said input and output coils, means connecting said tertiary coil in series witha load in the work circuit as well as with the alternator whereby the output potential of said transformer output coil is modified directly in response to variations of load in the work circuit supplied by the alternator; a regulator the field of which is connected to said output coil for receiving alternating current of variable magnitude therefrom, and means in said regulator connected to said auxiliary field of said exciter for rectifying the alternating current of variable magnitude derived from the al.- ternator work, circuit by said "current transformer and for reducing the field strength of said exciter by applying the same as a rectified, pulsating direct current of variable magnitude to said auxiliary field. r

In an automatic voltage control system for alternators, the combination of an exciter including an auxiliary field for supplying direct current orvariable magnitude to the field ofan alternator, anda regulator. including a rectifying commutator for supplying a pulsating direct current of variable magnitude to said auxiliary field of said exciter; said regulator including two pairs of opposed field poles the faces of which are of predetermined length and dimensions, said poles being spacedequidistantlyapart about the armature of said regulator-.toprovide equal spaces therebtween; each of said spaces being two-thirds the length of the face of afield pole, andua concentrated:armaturewinding on the armature of said regulator dividedinto four separate coils each of which has a dimension substantially equal to the dimension of a field pole face; said four armature coils being spaced equidistantly apart on the regulator armature.

4. A regulator for analternator, said regulator comprising a rectifying commutator consisting of a pair of opposed field poles having faces of predetermined area; said field poles being arranged so as to provide equal spaces therebetween each of which is approximately two-thirds-the length of a field pole face," an armature, and. an armature winding on said armature divided into separate coils equidistantly spaced'apart and each of which has a length approximately equal to the length of a field pole' face.

i FENTON F. HU'rcHINsoNr 

